NEW YORK (AP) — Federal inspectors have not determined whether human error was the cause of a New York train derailment that killed four people last month.

A two-page preliminary report issued Tuesday by the National Transportation Safety Board also does not address whether improved technology should have been in use when the Metro-North commuter train derailed Dec. 1 in the Bronx.

NTSB spokesman Keith Holloway said the agency’s determination of a probable cause could be a year or more away.

“It’s still early in our investigation so we don’t know what the final cause will be,” Holloway said.

The preliminary report restates previous findings that the train was traveling at 82 mph on a curve in the Bronx that had a 30 mph speed limit. It also repeats that no mechanical problems have been found.

Representatives of the train’s engineer, William Rockefeller, have said he may have lost focus at the controls in a momentary daze before the crash. The report does not address the issue.

Holloway said a transcript of what Rockefeller — and other crew members — told the NTSB would probably be released before the final report.

He said that report would probably address whether existing technology might have prevented the derailment. The NTSB has already said that a system called positive train control, which has not yet been installed, probably would have stopped the train.

A week after the derailment, Metro-North adjusted its signaling system so trains that are going too fast as they approach the bend near the Spuyten Duyvil station would trigger an alarm and an automatic braking system.

Metro-North is also using more plainclothes spotters who check that train operators are complying with all rules. Its president has announced his retirement. In a statement Tuesday, the railroad said it has also dropped some speed limits and improved speed monitoring.

The Federal Railroad Administration is conducting a two-month examination of the railroad’s safety compliance and safety culture. U.S. Sens. Charles Schumer, D-NY, and Richard Blumenthal, D-Conn., said Tuesday that the proposed federal budget includes funding for 45 new FRA inspectors.